I need to send a variable from Teamcity to Octopus Deploy, to use it there in a PowerShell script

I have tried to send it using "Additional command line arguments" in the step "Build Step: OctopusDeploy: Create release", using --variable "OctopusRegistry=Snapshot" in Teamcity

But when I try to show it using Write-Output "OctopusRegistry: $OctopusParameters["OctopusRegistry"]" in a powershell script in Octopus I get the following error:

OctopusRegistry: System.Collections.Generic.Dictionary`2[System.String,System.String]

Thanks!